Roasting of plumbiferous pyrites



Feb. 19, 1935. Kl w YOUNG 1,992,049

ROASTING OF PLUMBIFEROUS PYRITES` Filed Jan. 2o, 1933 Pam-infra KENNETH Wl LLtAM YGUNG ATTORNEY.

Patented Feb. 19, 1935 umi-i;mmse

4PA'IENr OFFICE Application January 20, 1933, Serial No; 652,773 In Great Britain January 23, 1932 5 claims. (o1, 23-134.)

This invention relates to processes for roasting or, burning sulphide ores such as pyritcs which contain smallV amounts (up to about 5 per cent) ofV of substantially the whole of the lead in theformv of leadsulphide; vThe lead sulphide may then be separated from the roasting gases by suitable reduction of temperature and collection of the lead sulphide fume in suitable'apparatus.

Accordingrto the invention, sulphide oressuch as pyrites containing small amounts of lead are subjected to roasting with a limited supply of air or oxygen-containing gasesin a rotary or shaft kiln orj'mechanical furnace so that the whole of the oxygen is used up and a portion of the heated material is in contact with gas free from oxygen. At the Sametime a stream of gas substantially free from oxygen, such as nitrogen or sulphur dioxide ora mixture of these, is introduced into the furnace at a suitable point, or points, preferably in the combustion zone. whereby lead sulphide is 'volatilized and carried 'off lin the' streamv of gases. l. Y ,jf

The temperature of the combustion zone in the furnace should be carefully controlled so that the combustion gases at a point, immediately above the combustion zone, at which they no longer con,- tain oxygen are at a sufficiently high temperature to volatilize the lead sulphide, whilstat the same time the temperature of the melting-point of the sulphide ore under treatment is not exceeded. Suitable temperatures are 80G-900 C. I have found that with pyrites containing up to 5 per cent. of lead substantially the whole of the lead is volatiliz'ed at temperatures of 80G-850 C.

VThe vapour pressure of lead sulphide at the temperatures employed is only small and it is therefore necessary to supply considerable quantities of gas, especially when the lead content of the sulphide ore is comparatively high. In general I have found that the quantityrof inert gas should be about twice that of the combustion air or gas and the rate of passage of the gasl through the burner should be about 20 centimetres` per second. Y

The absence ofy appreciable quantities of free oxygen in the zone where volatilization of the lead takes place isessential in order to avoid the combustion of'lead sulphide to leadA oxide. In the" case of an ore or material containing `such p'yrites this is insured by controlling the'rate of air supply. For materials poorerinsulphur and also in general it may be desirable to'add to the ore a small quantity of coke or other carbona-Y` ceous material in order to ensure the early re` moval of free oxygen. Under such circumstances sorne free sulphur may be present'in the gas and thisis a guarantee that the conditions are nonoxidizing.'` Such free Vsulphur may Ybe collected from the gas bylsuitable means afterremoval of the lead sulphide. I

The oxygen free gas maybe"` introduced 'together with air or oxygen-containing gas into the lower part of the furnace, or part or the whole of it may -be introduced directly into thecombustion zone. 'I'he gas introduced `mayin addition vbe employed'to control the temperature conditions in the manner Vdescribedin British Patent No. 359,478. When the content of lead is relatively high,` the amount of gas required to volatilize the leadv sulphide and carry it through the cooler regions at the top of the burner is comparatively large and in such cases, owing to too great a cooling effect, it will be necessary to preheat the gas whether it is introduced into the lower part of the furnace or into the combustionzone. Similarly in the case Vof a minimum amount of air or oxyg'en' being used for the combustion in order to obtain an increasedquantity of free sulphur in the gasesrproduced, a suiciently high temperature to volatilize the lead sulphide may not be lreached unless the introduced gases are preheated.

'with or without preheating, either to the combustion zone or partly to the combustion zone and partly to the lower part of the burner where they are mixed with the air or oxygen-containing gas.

The attached drawing shows a diagrammatic W sheet of the process of this invention.

. Example In the treatment of a pyrites containing 2 per cent of lead and 45 per cent of sulphur the process may be carried out as follows:- n

The pyrites'` inv coarsely ground' formis mixed with 10"per cent'of'its' Weight ofipowdered Acoke and the mixture is fed continuously into the upper end of a rotary kiln at the rate of 100 kg. per`xl hour. Air is blown into the lowerA end of the-'kiln7 at a rate corresponding to cubic metres per 100 kg. of the pyrites. At apoint above-'one-tlirdi the length of the kiln from the lower: :endramixf ture .of N2 and SO2 is introduced atsucha rate" that the maximum temperaturesinthefkiln does' not exceed 900 C. This gas is int`rodi1'ced ata-fy temperature of 200 C. and from 200 to. 300 cubic.

metres per 100 kg. of pyrites will be required ac` cordingtothe rate of. heat loss from the kiln. Under these conditions lthe pyrites is subjectedto. strongly reducing conditions in the upper endof ther-kiln and v:the exit'gas consists of amixture of N2; $92,. sulphur vapour andvCOzVtogether. with the Vapourof lead sulphide 'Ihegaslis cooledto about 4009 C vandpassed through an electrostatic dust-precipitator.- Here a dust is collected which is-rich-in lead sulphideand which may be disposed otter-.Worked up forthe .recoveryk of leadinany known manner. The residual-gas aftercom-plete cooling tocondensethe sulphur vapour' is .concentrated infSOz and. then .returned yto thepyrites burner'. -In .the concentration sucient nitrogen isfpurgedto correspond-to the nitrogen contained in the-air introducedinto the burner. Y

The: processaccording to the invention. may advantageously be combined with the. process for the sulphatization of zinc andy copper Vin 'sulphidefores describeddn my coV-pendingBr-itish application No.l 34770-/31 issued as Patent.A No. 395,760 Thus inthe combinedfprocessthe sulphur dioxide containingy gases( issuing: fromthe upper vportionofthe burner maybe enrichedvin sul-phurdioxide in` any desired manner andrecirculated, vafsuificient quantity of fgas .being passed through theburner orthe upperjpartoffit to volatilize the lead sulphide. If .the temperatureof vthe combustion .zone is kept sufficiently highfi. ennot lower than-850 C., andthe velocity and quantity of theg-asare suiiiciently great (depending upon the quantity of lead/contained inthe ore) substantiallyl the Whole of the lead will beremoved asleadfsulphide. inthe issuing gases.

The treatment of Ythe ore may also -becarried out.-so as to eiect the recovery ofthe sulphurfin the free state. For this purpose the conditions of roasting are strongly reducing and free carbon may be added in suitable form to assist in the reduction of sulphur dioxide to free sulphur. In general the methods described in British Patent No. 359,478 and'in co-pending Britishvapplication No. 2879/31 issued as Patent No. 39.1,136 may be employed; with' such modiicati'ons;v are described above to ensure l'the'completervolmziliza.- tion of the lead.

I- c1aim:- l

l; Aprocess.for the recovery of lead sulphide from iron sulphide ores containing small amounts g of-fleadwhieh comprises roasting said ore with a lin'ited supplyfof-airso that the whole of the oxya-portion. off heated material'is in contactr withgasffree from oxygen, introducing a stream Y of gas substantiallyv free from oxygen in sulcient quantityand at a suiiicient velocity and maintained. at a suflicient temperature to. volatili-ze 1 substantially the' whole of "th'el lead 4sulphide and remove itin the for'mof "vapour, cool-ingthe 'exit gases. and.' collecting.. the precipitated lflead sul# phide,

2. In a process of`roasting an ironlsuldeoie.

to bur-n all.. the ironsullde'intofiron oxiddanrlY sulfur dioxide; moving said-ore in counter current to saidgas, establiShi-nga zoneinsaidfurn'ace near. the entranceofV said ore. in whichjlie. un,

roastedY ore-is maintained vat' a. temperature of about 800'y to.90`0 C; and in-which the gases in Contact with the ore are ,substantially non-.ozb dizing, introducing.. intoV said furnace.v a. second streamof 'gas which .isirfree from oxygen,.. the amount-of V'saidlsecon'd gas beingv .at least `about twice that of the ist gas stream` and .-maintai? ing the gasflcw through said' furnace at arate of "at least" about L20. centimeters per second..

3". Th'e process. ofv claim 2'in which the gas stream leaving the furnace is treated 'to yprecipi; tate andrecove'r the `volatilizedlead`su1del con'- taiiiedltlierein.

4;"Th`e. process-'ofclaiin 2. in whch'a solidcarbonaceou's material is' mixed 'with the ore fd'int the furnace. i l i 5'. The process fof claim 2v which the second gas'strearn is" preheated.

. KENNETH WILLIAM YOUNG.

CERTIFICATE 0F CRRECTIQN.

Patent No. 1,992,049. February 19, 1935.

KENNETH WILLIAM YCUN G.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page I, second column;y

line 8, for "such" read much; page 2, first column, line 14, for "above" read about; and second column, line 7, for "2879/31" read 28729/31; and that the said Letters Patent should be read with these corrections therein that the same may* conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of June, A. D. 1935.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

